1. Field of the Invention
The present invention relates to a liquid discharging head, a liquid dicharging apparatus and a liquid discharging method for discharging desired liquid by applying thermal energy to the liquid, and more particularly to a liquid discharging head, an element substrate, a liquid charging apparatus and a liquid discharging method capable of discharging two or more liquid droplets in succession from a discharge port.
The present invention is applicable to various apparatus such as a printer for recording on media such as paper, yarn, fiber, textile, leather, metal, plastics, glass, wood, ceramics etc. a copying machine, a facsimile having a communication system, or a word processor having a printer unit, or to industrial recording apparatus coupled in complex manner to various processing apparatus.
In the present invention, xe2x80x9crecordingxe2x80x9d means not only providing a recording medium with a meaningful image such as a character or an image but also providing with a meaningless image such as a pattern.
2. Related Background Art
There is already known a liquid jet recording method, so-called bubble jet recording method, in which energy such as heat is given to ink (liquid) to generate a rapid state change therein and the liquid is discharged from a discharge port by an action force resulting from such state change for deposition on a recording medium thereby forming an image. The recording apparatus utilizing such bubble jet recording method is generally provided, as disclosed in the U.S. Pat. No. 4,723,129, a discharge port for discharging the liquid, a liquid flow path communicating with the discharge port, and an electrothermal converting member constituting energy generating means for discharging the liquid present in the liquid flow path.
Such recording method has various advantages such as ability of recording high quality image with a high speed and with a low noise level, and ability for recording the image of a high resolution or even a color image with a compact apparatus, since discharge ports for discharging liquid can be arranged with a high density in the head for executing such recording method. For this reason, the bubble jet recording method is recently employed in various office equipment such as a printer, a copying machine, a facsimile etc. and is being adopted also in industrial system such as a text printing apparatus.
FIG. 23 is a schematic cross-sectional view around the electrothermal converting member of a conventional liquid discharge head for executing the recording by such recording method. In the illustrated example, the electrothermal converting member is composed of a resistance layer 100 and electrodes 101a, 101b laminated thereon and mutually spaced as a pair. Thus a heat generating portion 105, for generating heat by voltage application, is formed between the electrodes 101a and 101b, and such portion constitutes a bubble generating area where a bubble is generated by film boiling. On the resistance layer 100 and the electrodes 101a, 101b, there are formed two protective layers 102, 103 for protecting these components.
A discharge oppening for discharging liquid by the generation of a bubble 104 by the heat from the heat generating portion 105 may be provided, as in a case of opening S, in a position opposed to the heat generating portion 105 (so-called side shooter), or in a lateral position as in a case of opening E (so-called edge shooter). In either case, the bubble 104 in such configuration of the liquid discharge head grows larger toward a liquid chamber X with a relatively smaller liquid flow resistance, so that a bubble vanishing position 106 is in the central part of the heat generating portion 105 or is somewhat displaced toward the liquid chamber.
Thus, in the liquid discharge head as shown in FIG. 23, the liquid is relatively strongly pushed back toward the liquid chamber X together with the growth of the bubble 104. Consequently a meniscus, formed at the discharge port and constituting an interface between the liquid and the external atmosphere, shows a relatively large retraction and a relatively large vibration by the bubble extinction after the liquid discharge. Also in the bubble vanishing process, there are generated a liquid flow from the liquid chamber toward the heat generating portion 105 and a liquid flow from the discharge port toward the heat generating portion 105 in an approximately same magnitude whereby the practical start timing of liquid refilling toward the discharge port becomes after the liquid flow from the discharge port is almost finished and is relatively late, so that a relatively long time is required until the meniscus returns to the normal state and becomes stabilized. For this reason, for discharging liquid in succession, there is required a relative long interval between the discharges and the drive frequency capable of satisfactorily discharging the liquid is inevitably limited.
For increasing the drive frequency in the liquid discharge head, the present applicant already proposes a configuration provided with a movable member provided in the bubble generating area and adapted to displace along with the growth of the bubble and a limiting portion for limiting the displacement of the movable member within a desired range, wherein the limiting portion is provided opposed to the bubble generating area in the liquid flow path and, by the substantial contact between the displaced movable member and the limiting portion, the liquid flow path including the bubble generating area becomes a substantially closed space except for the discharge port. In such liquid discharge head, at the growth of the bubble, the movable member so displaces as to substantially close the liquid flow path at the upstream side of the bubble generating area, so that the liquid pushed back toward the upstream side at the bubble growth is relatively limited. At the bubble vanishing, the movable member so displaces as to reduce the liquid flow resistance at the upstream side, so that the bubble vanishing at the upstream side of the bubble generating area is accelerated and proceeds faster than in the downstream side. Therefore, the meniscus shows a smaller retraction and the liquid refilling is executed efficiently.
Also in the liquid discharge head, gas dissolved in the liquid may be released at the bubble generation to form a microbubble which may remain in the liquid flow path. In order to prevent defective discharging operation resulting from a large amount of such remaining microbubbles, there is periodically executed a recovery operation of sucking out the liquid in the vicinity of the discharge port thereby removing the microbubbles. On the other hand, in the liquid discharge head provided with the movable member, since the liquid is pushed back little to the upstream side, the microbubbles are emitted from the discharge port before they increase to a level hindering the liquid discharging operation and remains little in the liquid flow path. For this reason the recording operation can be executed continuously for a relatively long period, in excess of 100 sheets at maximum.
As explained in the foregoing, the liquid discharge head with the movable member, capable of rapid liquid refilling without a large retraction of the meniscus, has advantages of executing the liquid discharge with a relatively short interval and enabling drive with a relatively high frequency.
In order to enable drive with a higher frequency, it is conventionally conceived that a faster extinction of the bubble, generated for the preceding liquid discharge, is practically effective. This is because, in order to achieve the succeeding discharge in satisfactory manner, it is conceived that the succeeding discharge has to be executed after the meniscus returns to the stationary state and is stabilized after the vibration process and after the liquid refilling is completed, and because such completion of refilling and stabilization of the meniscus are achieved by the completion of the bubble vanishing.
However the bubble vanishing theoretically requires a certain time for completion, and such time results in a limit in the driving interval. More specifically, by applying a voltage pulse of a duration of several microseconds for the liquid discharge, the period required for generation, growth and vanishing of the bubble of the bubble can be made 30 to 50 xcexcsec from the start of pulse application, in consideration of the delay in response. Consequently, the drive frequency is limited to 20 to 30 kHz if the next discharge is executed by applying a pulse immediately after the bubble vanishing. Therefore the present inventors have executed intensive investigation, considering that the technology cannot be advanced unless such reality is broken through, and have reached a novel liquid discharge method capable of liquid discharge in succession at a high frequency.
In the following there will be explained the novel liquid discharge method of the present inventors.
The novel liquid discharge method employs a liquid discharge head provided with a heat generating member for generating thermal energy for generating a bubble in the liquid, a discharge port for discharging liquid, a liquid flow path communicating with the discharge port and having a bubble generating area for generating a bubble in the liquid, a liquid chamber for supplying the liquid flow path with the liquid, a movable member provided in the bubble generating area and adapted to displace along with the bubble growth, and a limiting portion for limiting the displacement of the movable member in a desired range, wherein the liquid discharged from the discharge port by the energy at the bubble generation. In such liquid discharge head, the heat generating member and the discharge port are in linear communication, while the limiting portion is opposed to the bubble generating portion of the liquid flow path, and, by the substantial contact between the displaced movable member and the limiting portion, the liquid flow path having the bubble generating portion becomes a substantially closed space except for the discharge port. In this liquid discharge method, in causing the same discharge port to discharge a plurality of liquid droplets in succession, driving energy for a succeeding liquid discharge is supplied to the heat generating member in a state where a bubble, formed for the preceding liquid discharge and being still in the course of vanishing, is present at the discharge port side of the bubble generating area and no bubble is present at the side of the movable member.
Thus, this novel liquid discharge method is not to execute the drive for the succeeding liquid discharge after the extinction of the bubble formed at the preceding liquid discharge, but a remarkable invention of executing successive discharge, utilizing the bubble formed for the preceding liquid discharge, at a timing in consideration of the balance between the bubble formation for the succeeding liquid discharge and the liquid discharge.
More specifically, the novel liquid discharge method of the present inventors, being based on the aforementioned movable member providing the efficient refilling characteristics and on a fact that the bubble vanishing position is at the discharge port side of the bubble generating area in the liquid discharge head having such movable member, is attained by a finding that there is a timing capable of achieving satisfactory liquid discharge in the course of vanishing of the bubble for the preceding liquid discharge utilizing the relationship between the bubble change and the meniscus position. In the liquid discharge head having the movable member, there exists a timing at which a bubble formed for the preceding liquid discharge and being in the course of vanishing process is present at the discharge port side of the bubble generating area but no bubble is present at the side of the liquid chamber. At such timing, the retraction of the meniscus has started but has not reached the maximum. Also since the bubble already vanishes at the movable member side of the heat generating member, the liquid refilling is substantially completed. At such timing, therefore, the liquid discharge head is in a state extremely advantageous for the next liquid discharge, and liquid discharge in succession can be satisfactorily achieved by supplying the heat generating member with the driving energy for the next liquid discharge at such timing. The successive liquid discharge at such timing corresponds to liquid discharge in succession with a much shorter interval, in comparison with the conventional case where the next liquid discharge is executed after the bubble vanishing is completed.
In this liquid discharge method, the drive energy for the next liquid discharge is supplied to the heat generating member while the bubble formed for the preceding liquid discharge remains partly, so that, in the second and subsequent liquid discharges, there is obtained a pre-heating effect by the thermal energy generated in the preceding liquid discharge, thereby reducing the time required by the bubble to grow to the maximum size. Thus, there can be obtained an advantage that the bubble formation for the succeeding liquid discharge can be achieved immediately. Also such pre-heating effect can improve the efficiency of energy for the succeeding liquid discharge. Also such pre-heating effect can increase the volume of the liquid droplet discharged at the second or subsequent discharge, in comparison with that of the liquid droplet discharged at the stationary state.
Furthermore, the liquid flow toward the discharge port, resulting at the refilling and generated by the bubble vanishing in the upstream side of the bubble generating area, can accelerate the liquid flow in the succeeding liquid discharge, whereby the velocity of the discharged liquid droplet at the second or subsequent liquid discharge can be made larger than that in the liquid discharge executed from the stationary state.
Such increase in the volume or velocity of the consecutive liquid droplets in comparison with the ordinary state provides an advantage suitable for multi-level recording. For example it is possible to vary the recording density by employing two successive discharges and varying the interval between such two discharges or by varying the number of successive discharges with a constant interval between the discharges.
As explained in the foregoing, the present liquid discharge method enables liquid discharges in succession with a very short interval. It is also possible to capture a satellite, formed by separation of a trailing portion of a liquid droplet in the preceding liquid discharge, by a liquid droplet in the succeeding liquid discharge. Such capture of the satellite by the succeeding liquid droplet is advantageous for executing the multi-level recording.
The capture of the satellite by the succeeding liquid droplet is achieved for the first time by the successive liquid discharges with a very short interval by the novel liquid discharge method proposed by the present inventors. This liquid dischrage method comprises a step of heating liquid in the liquid flow path with a heat generating member thereby generating a bubble in the liquid, and a step of causing a discharge port communicating with the liquid flow path to discharge liquid thereby forming a liquid droplet by the energy at the bubble generation, wherein these steps are repeated plural times to discharge a plurality of liquid droplets in successive manner, and is featured by a fact that a satellite is captured by a liquid droplet discharged by the succeeding liquid discharge and is integrated with such liquid droplet.
The satellite becomes substantially spherical by surface intension in the course of flying, but, in the present liquid discharge method, the capture by the liquid droplet can be made while the satellite is still in a liquid rod shape immediately after formation of the satellite, and such fact also features the present liquid discharge method.
In case of applying the above-described novel liquid discharge method by the present inventors to a liquid discharge apparatus such as an ink jet recording apparatus, it is necessary to investigate the mode of supply of the drive signal to the liquid discharge head (ink jet recording head in case of an ink jet recording apparatus). In the following there will be considered a case where the liquid discharge apparatus is an ink jet recording apparatus having a liquid discharge head constituting an ink jet recording head.
In general, the ink jet recording apparatus executes recording by reciprocating the ink jet recording head, having a plurality of discharge ports for discharging liquid (ink), in a main scanning direction, while a recording medium such as paper or fabric is conveyed in a sub scanning direction. Therefore, the drive signal to the ink jet recording head is supplied from a main body of the apparatus to the ink jet recording head through a flexible cable. As the above-described liquid discharge recording is capable of high definition recording, the ink jet recording head is usually provided with several hundred discharge ports and heat generating members of a corresponding number. The heat generating members are collectively prepared in a required number by a thin film process (semiconductor manufacturing process) on an element substrate (also called heater board) composed of a semiconductor substrate such as of silicon.
It is not practical to provide a signal line for each heat generating member, for supplying a driving pulse thereto, and to connect the ink jet recording head and the main body of the apparatus by such signal line, because the number of such signal lines is too large and a circuit to be provided in the main body of the apparatus for driving the heat generating members becomes bulky. Therefore, also in the conventional ink jet recording apparatus, there is employed a method of multiplexing the drive signals for the heat generating members for transmission from the main body of the apparatus to the ink jet recording heat and demultiplexing such signals in the recording head, for selectively driving the heat generating members. Also there is employed a configuration of selectively driving the heat generating members by incorporating such heat generating members in a diode matrix.
Such demultiplexing circuit or the diodes constituting the diode matrix may be provided independently in the ink jet recording head, but, since the element substrate itself on which the heat generating members are formed is composed of a silicon semiconductor substrate, these members are usually formed on such element substrate.
As a result of investigation, however, the conventional configuration in which the demultiplexing circuit or the diode matrix is incorporated in the ink jet recording head is unable to fully exploit the features of the liquid discharge method newly proposed by the present inventors.
In this novel liquid discharge method, the discharge can be repeated from a discharge port (nozzle) with a frequency of several hundred kHz. Consequently the repeating period of the drive pulse applied to the heat generating member becomes about 10 xcexcs at shortest, and, since the duration of the drive pulse is not much different from that in the conventional ink jet recording head, the duty ratio of the pulse becomes larger than in the conventional configuration and it becomes difficult for a simple diode matrix to drive the ink jet recording head having many discharge ports. Also in a configuration of transmitting the drive signals to the ink jet recording head after multiplexing, with the simple multiplexing of the signals for individually driving several hundred heat generating elements for example with a drive frequency of 100 kHz, the frequency of the signal after multiplexing becomes as high as several ten MHz, eventually resulting in a phenomenon that the data transfer cannot be executed in time. Also the flexible cable connecting the ink jet recording head and the main body of the apparatus has large impedance and parasite capacitance, so that the heat enable signal for driving the heat generating member may become distorted.
Furthermore, the novel liquid discharge method enables the multi-level recording by regulating the interval of the two successive discharge pulses or by varying the number of the liquid droplets discharged in succession as explained in the foregoing, but the conventional multiplexing method or the method utilizing the diode matrix is unable to handle such multi-level recording.
In order to achieve multi-level recording, it is necessary to provide each heat generating member with drive pulses of a matching number, and the multi-level recording, if tried with an extension of the conventional technology, requires an excessively high frequency in the signal from the main body of the apparatus to the recording head or an excessively large magnitude of the circuit to be incorporated in the recording head (element substrate), leading to a limitation in the chip area.
The multi-level recording can also be achieved in a discharge method other than the above-described liquid discharge method, namely in case of utilizing an energy generating element for discharging liquid from a discharge port, by discharging a plurality of liquid droplets. However, even in such case, there will be encountered drawbacks such as an excessively high frequency in the signal from the main body of the apparatus to the recording head or an excessively large magnitude of the circuit to be incorporated in the recording head (element substrate), leading to a limitation in the chip area.
Stated differently, there are strongly desired a liquid discharge head capable of multi-level recording with a limited number of the signal lines and with the signal of a relatively low frequency and also capable of reducing the magnitude of the circuit to be incorporated in the element substrate, and an element substrate to be used in such liquid discharge head.
In consideration of the foregoing, the object of the present invention is to provide a liquid discharge head suitable for various liquid discharge methods such as the novel liquid discharge method proposed by the present inventors and also for multi-level recording and capable of discharging liquid from the discharge ports by receiving a drive signal of a relatively low frequency, an element substrate adapted for use in such liquid discharge head, a liquid discharge apparatus utilizing such liquid discharge head, and a liquid discharge method utilizing such liquid discharge head.
A first liquid discharge head of the present invention comprises a plurality of heat generating members for generating thermal energy for generating a bubble in liquid, a discharge port provided for each heat generating member and constituting a portion for discharging the liquid, a liquid flow path communicating with the discharge port and having a bubble generating area for generating the bubble in the liquid, a movable member provided in the bubble generating area and adapted to displace along with the growth of the bubble, a limiting portion for limiting the displacement of the movable member within a desired range, and a circuit receiving data of a predetermined number of bits for each heat generating member and generating a drive pulse for the corresponding heat generating member based in the received data, wherein the heat generating member and the discharge port are in a linear communication state, the limiting portion is so provided as to be opposed to the bubble generating area in the liquid flow path, the liquid flow path including the bubble generating area reaches a substantially closed space except for the discharge port by the substantial contact between the displaced movable member and the limiting portion, the number of the drive pulses generated from the received data is larger than the aforementioned predetermined number of pulses at least for one of the aforementioned data, and the liquid discharged from the discharge port by the energy of bubble generation by the application of the drive pulse.
A second liquid discharge head of the present invention comprises:
a plurality of discharge ports constituting portions for discharging liquid;
an energy generating element provided for each discharge port, for generating energy for discharging the liquid; and
a circuit for receiving an input of data of a predetermined number of bits, at least equal to 2 bits, for each energy generating element, and converting the entered data to generate a drive pulse for the corresponding energy generating element;
wherein the liquid is discharged from the discharge port by the energy generated by the application of the drive pulse to the energy generating element.
A third liquid discharge head of the present invention comprises a plurality of discharge ports constituting portions for discharging liquid, an energy generating element provided for each discharge port, for generating energy for discharging the liquid, and a circuit including a shift register for receiving serial data of a predetermined number of bits for each energy generating element and extracting, from the serial data, data for each energy generating element in the form of parallel data, a data decoder for decoding the parallel data and a logic circuit for generating a drive pulse for each energy generating element from a reference pulse based on the output of the data decoder, wherein the liquid is discharged from the discharge port by the energy generated by the application of the drive pulse to the energy generating element.
A first element substrate of the present invention integrally comprises a plurality of energy generating elements for generating energy for generating a bubble in liquid, a shift register for receiving serial data of a predetermined number of bits for each energy generating element and extracting, from the serial data, data for each energy generating element in the form of parallel data, means for decoding the parallel data for each heat generating member, and means for receiving a heat pulse and generating a drive pulse from the heat pulse according to the result of decoding, thereby applying the drive pulse to the corresponding energy generating element.
A second element substrate of the present invention integrally comprises a plurality of energy generating elements for generating energy for generating a bubble in liquid, a shift register for receiving serial data of a predetermined number of bits for each energy generating element and extracting, from the serial data, data for each energy generating element in the form of parallel data, and means provided for each heat generating member and adapted for generating drive pulses of a number represented by the corresponding parallel data for application to the corresponding energy generating element.
A third element substrate of the present invention integrally comprises a plurality of energy generating elements for generating energy for generating a bubble in liquid, a shift register for receiving serial data of a predetermined number of bits for each energy generating element and extracting, from the serial data, data for each energy generating element in the form of parallel data, and means provided for each heat generating member and adapted for generating two drive pulses with an interval represented by the corresponding parallel data for application to the corresponding energy generating element.
A liquid discharge apparatus of the present invention comprises a carriage for supporting the above-described liquid discharge head of the present invention, wherein the serial data are transmitted to the liquid discharge head to discharge liquid droplets therefrom while the carriage is moved according to the recording information.
A liquid discharge method of the present invention comprises discharging a plurality of liquid droplets in succession from a same discharge port with a liquid discharge head including a heat generating member for generating thermal energy for generating a bubble in liquid, a discharge port constituting a portion for discharging the liquid, a liquid flow path communicating with the discharge port and having a bubble generating area for generating the bubble in the liquid, a movable member provided in the bubble generating area and adapted to displace along with the growth of the bubble, a limiting portion for limiting the displacement of the movable member within a desired range, and a circuit receiving data of a predetermined number of bits for each heat generating member and generating a drive pulse for each heat generating member based on the received data, wherein the heat generating member and the discharge port are in a linear communication state, the liquid is discharged from the discharge port by the energy at the bubble generation, the limiting portion is so positioned as to be opposed to the bubble generating area of the liquid flow path, and the liquid flow path including the bubble generating area reaches a substantially closed space except for the discharge port by the substantial contact between the displaced movable member and the limiting portion, wherein the drive energy for the next liquid discharge is supplied to the heat generating member in a state where a bubble formed for the preceding liquid discharge and in the course of vanishing is present at the discharge port side of the bubble generating area and no bubble is present at the movable member side.